1. Field
This disclosure relates generally to semiconductors, and more specifically, to storage circuits that are susceptible to soft errors.
2. Related Art
High energy neutrons are well known for having an adverse effect on the performance of semiconductors. High-energy neutrons bombard our planet from sources originating in deep space. As the neutrons enter earth's atmosphere they collide with a large amount of particulate matter and are split into multiple neutrons. While some energy is lost from the collisions, the sheer number of neutrons reaching ground level is noticeably increased. The neutrons lose energy in semiconductor materials through collisions with silicon nuclei that lead to a chain of secondary reactions. These reactions deposit a track of electron-hole pairs as they pass through a p-n junction. Some of the deposited charge recombines while some of the charge collects at p-n junction contacts. When a neutron particle strikes a sensitive region of a data storage circuit, such as at the gate of a charge storage device, the electrical charge that accumulates could exceed the minimum charge that is needed to reverse the data value that is stored in the data storage circuit. Reversal of stored data values is conventionally referred to as a “soft error”. The term “SER” is referred to as a soft error rate. It is well documented that this effect varies with both latitude and altitude. Thus aviation electronics and other safety-critical applications are significantly impacted by the presence of soft errors. As integrated circuit dimensions continue to decrease, the incidence of soft errors is increasing. As a result, radiation induced soft errors are one of the main contributors to failure rates in high speed data processors and communications chips.
Other sources of soft errors are varied and include alpha particles which may be emitted by trace amounts of radioactive isotopes present in packing materials of integrated circuits. Alpha particles are capable of disturbing up to a five micron area of silicon and can readily modify the programmed state of a data storage device. Additionally, the conductive alloys that are used for the conductive bump in flip-chip packaging have also been identified as a possible source of alpha particles. Various semiconductor processes also tend to exhibit differing degrees of susceptibility to soft errors. For example, silicon-on-insulator (SOI) processes tend to be more reliable because charge that is dissipated into the substrate does not make it back into the glass insulator material to cause charge disturbances.